1. Field of the Invention
Aspects of the present invention relate to a can for a cylindrical lithium rechargeable battery, and a cylindrical lithium rechargeable battery using the same.
2. Description of the Related Art
Generally, the need for weight-reduction and high performance in wireless portable devices, such as, camcorders, cellular phones, notebook computers, and others, has led to research into secondary batteries used as power supplies. Such secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries, and others. In particular, lithium secondary batteries can be recharged, and are capable of realizing a size-reduction and a high capacity. Since lithium secondary batteries have a high operating voltage and a high energy density per unit weight, they are widely used in high-tech electronics.
FIG. 1 is a vertical-sectional diagram illustrating a related art cylindrical lithium rechargeable battery.
Referring to FIG. 1, the cylindrical lithium rechargeable battery 100 includes an electrode assembly 110, a cylindrical can 130 which accommodates the electrode assembly 110 and an electrolyte solution, and a cap assembly 150 that is assembled on the upper portion of the cylindrical can 130, so as to seal the same, and allows an electric current generated in the electrode assembly 110 to flow out of the device.
The electrode assembly 110 is formed by winding a cathode plate 112 in which the surface of a cathode collector is coated with a cathode active material, an anode plate 114 in which the surface of an anode collector is coated with an anode active material, and a separator 113 which is interposed between the cathode plate 112 and the anode plate 114 to provide an electrical insulation therefore, into a jelly-roll type configuration. Although not shown in the drawing, the cathode plate 112 includes a cathode collector made of a thin metal sheet with an excellent electric conductivity, such as, an aluminum (Al) foil, and a cathode active material layer coated on both surfaces thereof. A cathode collector region without a cathode active material layer, that is, a cathode uncoated portion, is formed at both ends of the cathode plate 112. One end of the cathode uncoated portion is attached with a cathode tap 116, which is generally made of an aluminum (Al) material, that extends a predetermined amount above the electrode assembly 110. Further, the anode plate 114 includes an anode collector made of a thin conductive metal sheet, such as, a copper (Cu) or nickel (Ni) foil, and an anode active material layer coated on both surfaces thereof. An anode collector region without an anode active material layer, that is, an anode uncoated portion, is formed at both ends of the anode plate 114. One end of the anode uncoated portion is attached to an anode tap 118, which is generally made of a nickel (Ni) material, and extends a predetermined amount below the electrode assembly 110. In addition, insulation plates 122 and 124 may be further formed on the upper and lower portions of the electrode assembly 110, in order to prevent each thereof from contacting the cap assembly 150, or the cylindrical can 130.
The cylindrical can 130 includes a cylindrical surface plate 142, with a predetermined diameter to accommodate the cylindrical electrode assembly 110, and a lower plate 131 to seal a lower portion of the cylindrical surface plate 142. An upper end portion of the cylindrical surface plate 142 has an opening through which the electrode assembly 110 is inserted.
The anode tap 118 is attached to the center of the lower plate 131 of the cylindrical can 130 so that the cylindrical can 130 acts as an anode. The cylindrical can 130 is generally made of aluminum (Al), iron (Fe), or an alloy thereof. Additionally, the cylindrical can 130 includes a clipping portion 146, which is bent inwardly from an upper end, so as to pressurize an upper portion of the cap assembly 146, when attached to the opening formed on the upper end thereof. Further, the cylindrical can 130 includes a beading portion 144, which is recessed inwardly, at a position apart from a lower portion of the clipping portion 146, by a distance corresponding to the thickness of the cap assembly 150, so as to pressurize a lower portion of the cap assembly 150.
The cap assembly 150 includes a safety vent 152, a current breaker 153, a secondary protection circuit 154, and a cap up 156. The safety vent 152 is formed into a plate shape, and placed at the lower portion of the cap assembly 150. The safety vent 152 has a central protrusion that curves down toward the electrode assembly 110. Herein, the curvature of the protrusion can be reversed by pressure generated from the inside of a rechargeable battery.
An anode tap 118 extends from the anode plate 114 to the lower plate 131. A cathode tap 116 extends from the cathode plate 112, and is welded to a predetermined position of a lower surface of the safety vent 152, so that the safety vent 152 and the cathode plate 112 of the electrode assembly 110 are electrically coupled to each other. The anode plate 114 is electrically coupled to the can 130, either via a tab (not shown) or by a direct connection method.
Generally, the anode tap 118 is welded to approximately the middle of the lower plate 131 of the can 130 by resistance welding. The welding is performed by inserting a first welding rod into the middle of the electrode assembly, so as to contact the anode tap 118. A second welding rod contacts a bottom surface of the lower plate 131, and then electric current is applied thereto. An electric current is applied to a plurality of conductors that contact each other, and heat is generated due to contact resistance, and such heat causes a welding of the conductors to occur. A large amount of the heat generation occurs in the contact region of the conductors, as the contact resistance is high. Such contact resistance is inversely proportional to the size of the contact region thereof.
However, since both of the anode tap 118 and the lower plate 131, according to the related art, are formed with flat surfaces, the contact area thereof is large, leading to a low contact resistance. Therefore, less heat from electricity applied by the welding rod is produced, thereby leading to a poor weld-ability.